Most of internal combustion engines mounted in vehicles are cooled with cooling water circulated by a water pump. The water pump is for example an electric-powered and thus driven water pump. The cooling water is used in order to prevent the engine from being extremely heated by the heat generated by the engine's combustion operation. On the other hand, when the engine has low temperature, in other words, when the cooling water's temperature is lower than a predetermined threshold value, the electric-powered water pump is stopped or intermittently stopped to allow the cooling water to be circulated at a limited flow rate to promote warming up the engine for stable combustion operation.
The temperature of the cooling water is not only used for controlling the electric-powered water pump but is also used for controlling the engine in various manners. However, when the water pump is stopped and the cooling water does not circulate, the cooling water at the location of a temperature sensor which measures the temperature of the cooling water and the cooling water at a location distant from the temperature sensor may exhibit a large difference in temperature. Then, the cooling water's temperature sensed by the temperature sensor may no longer reflect the actual temperature of the engine, and the engine may no longer be controlled appropriately.
To address this issue, Japanese Patent Laying-Open No. 2008-169748 (Patent Literature 1) discloses operating an electric-powered water pump for a predetermined period of time if cooling water is lower in temperature than a predetermined threshold value and the electric-powered water pump should be stopped. This can reduce the cooling water's variation in temperature and allows the cooling water's temperature to be understood appropriately.